1. Field of the Invention
The present invention relates to a tire for use on motor vehicles, trailers, motorcycles, aircraft or similar (referred to generally as “vehicles” in the following text), provided with an electricity generator which can supply sensors and any other circuits incorporated in the said tire, the generator having no galvanic contact with fixed or rotating components present in the vehicle. In particular, the invention relates to a tire in which the unit formed by one part of the generator, the sensors and the bead wire constitutes an assembly to be incorporated in the carcass of the tire during its manufacture.
The invention also relates to a method for the manufacture of the said tire.
2. Description of the Related Art
The structure of an ordinary tire essentially comprises a carcass provided with at least one piece of reinforcing rubberized fabric, or carcass ply, each of whose edges is fixed to at least one circumferentially inextensible annular metal core, commonly known as the bead core, which is the reinforcing member which keeps the tire on its mounting rim. The carcass is completed by a pair of sidewalls, in axially opposing positions, and a tread strip disposed on the crown of the casing and impressed with a relief pattern which imparts to the tire particular qualities of behaviour in use. The tire can also be provided with a belt structure, normally produced with rubberized fabrics incorporating metal reinforcing cords, interposed between the carcass and the tread band.
Circuits comprising encoders and/or sensors, connected to transponders (which receive signals and transmit responses), supplied by induction, and housed within vehicle tires or wheels, have been known for some time.
For example, patent application WO 90/12474, having the title “Vehicle tire identification system”, describes a system consisting of a transponder located within a tire, supplied by a winding disposed in the crown portion of the tire, or at least situated in a position remote from the bead cores of the said tire (p. 5, lines 20-22).
This winding is supplied by induction with an alternating current of suitable frequency by means of a large excitation winding which is disposed outside the tire and carried by a scanning tool such as a bar, or located in a fixed place, for example in the road surface, and which is brought close to the equator of the tire where the said transponder supply winding is housed.
In the absence of information on this matter, the applicant considers that this arrangement remote from the bead cores is due to the necessity of preventing the reduction of the efficiency of the winding by parasitic currents which would be generated in the bead core by the inductive coupling between the bead core and a winding disposed in its vicinity. An advantage of the system described is the fact that the transponder supply winding, because of its dimensions, operates even if the winding of the scanning tool is not disposed in its immediate vicinity, whereas the latter arrangement is necessary if the supply winding has a small diameter and is situated in a closely defined point of the crown or of the sidewall of the tire.
However, the device proposed in patent application WO 90/12474 has at least the following drawbacks:    a) it requires transponder supply windings positioned close to the equator of the cover, in other words just under the tread band or in its immediate vicinity, to minimize the losses of efficiency of the said windings due to the presence of the bead cores. This greatly complicates the tire production process and has the further disadvantage of potential structural problems due to the presence of the winding in a part of the tire subject to considerable stresses and deformations when in use;    b) it necessitates the installation of the device using the power generated by the winding in the same highly mechanically stressed part of the cover where the winding is located, or, alternatively, the incorporation in the tire sidewall structure of electrodes to transfer the said power to a more suitable position for its use.
Another example is provided by U.S. Pat. No. 5,181,975, which describes a transponder supplied by a winding which is situated in the bead of the cover, and is separate from the bead core but inductively coupled to the bead core; the currents induced in the bead core by an external magnetic field which varies in a sinusoidal way induce, in turn, voltages in the transponder supply winding.
This location of the secondary winding (inductive antenna), like the location in the crown described previously, offers the advantage of always having a good inductive coupling to the primary winding (transmitter). However, this solution also presents problems in respect of both the mechanical characteristics of the tire (with a substantially inextensible turn housed in a particularly complex and partially deformable structural area, namely the bead area) and its manufacturing process.
U.S. Pat. No. 4,006,449, having the title “Information detector for a tire wheel”, describes a system of supplying a sensor of tire operating parameters, such as internal pressure and/or temperature, consisting of a winding comprising a specified number of turns located on the edge of the rim in a radially inward position with respect to the axis of rotation of the wheel.
The winding is connected to a passive transducer (the sensor) which communicates with the interior of the tire, being located in the sealing cap of the air filling valve of the said tire. The said circuit receives an excitation signal induced by a first coil fixed to the chassis of the vehicle and connected to an alternating current source which is also fixed to the vehicle; the impedance of the said coil depends on the passive transducer, since the latter affects the strength and/or phase of the excitation signal.
A second fixed coil, inductively coupled to the turns of the rotating winding, senses the said variations of amplitude and/or phase and is connected to a circuit for processing the sensed signals, which controls both an indicator of the sensed values and any provided alarm devices which are activated in the presence of anomalous values of the parameters, such as a loss of pressure in the tire due to a puncture or fault in it.
This system would behave in a fairly satisfactory way, producing on the dashboard of a vehicle reliable information on the operation of the tires, combined with warnings of dangers due to anomalous situations, if it did not have an intrinsic weakness consisting in the flexible connections between the circular winding located on the rim and the transducer located within the cap of the air filling valve. These connections, being affected both by the centrifugal stresses caused by the rotation of the wheel and by the stresses due to the inevitable impacts of the wheel against accidental obstacles (when running over broken ground, pavements, etc.), are subject to frequent rupture.
U.S. Pat. No. 4,717,905, having the title “Warning system including means for remotely energizing condition sensing device”, describes a system for remotely supplying at radio frequency one or more devices for sensing state conditions, such as the internal conditions of tires, wherein a radio signal generated by a radio-frequency source is received by a circular coil antenna installed on the rim of the wheel of a vehicle and is used to supply one or more transducers of physical values, for example pressure, connected to the antenna. The transducer varies the resonant frequency of the oscillating circuit comprising the antenna installed on the rim as a function of the value of the physical quantity which is being monitored; the variation of the resonant frequency is sensed by circuits associated with the radio-frequency generator and can then be used to control instruments and alarms on the dashboard of the vehicle.
The principal disadvantages of the described system are inherent in the geometrical and mechanical design of the system: the coil antenna mounted on the rim has to be electrically connected to the sensors incorporated in the tire, with the usual problems related to the low reliability of connectors which have to be incorporated in parts subject to large deformations, such as the structural components of tires.
The examination of the prior art as described above reveals that there is not yet available a simple and reliable electricity generator which is capable of supplying sensors of operating parameters of the tire or other devices and which does not use electrical connections, particularly those with equipment fixed outside the tire, with all the problems associated with them.